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Stressed frogs that smell like cashew nuts or curry, and a 76-year-long laboratory experiment, have earned Australian scientists Ig Nobel prizes this year.

The 2005 Ig Nobel Prizes, which honour "achievements that first make people laugh, and then make them think", have just been presented by a team of Nobel laureates at a US gala ceremony at Harvard University.

Associate Professor Mike Tyler's team from the University of Adelaide, wins the Ig Nobel biology prize for its work on frog smells.

Tyler says each frog has a characteristic odour when stressed.

"Most of the tree frogs have odours which resemble either peanuts or cashew nuts," he says. "It's very sweet."

He says another group of frogs have a distinct curry smell.

"In fact one is a sweet Bombay curry," he says. "And there's another one which is more like one of the north Indian chilli-laden curries."

Tyler and team have also found about 20 frogs that smell like cut grass and then "there are some rancid ones".

The researchers aren't sure what all the smells mean but have found out that some of the chemicals behind them are responsible for killing mosquitoes.

They also found that some chemicals stop pigeons pooping on parapets and are already used as a bird repellent in London, Paris and New York.

Watching paint dry

Professor John Mainstone and the late Professor Thomas Parnell of the University of Queensland in Brisbane win the Ig Nobel physics prize.

Mainstone says in 1927 Parnell started what has now become the longest ever running laboratory experiment, involving ultra-slow moving drops of black tar or pitch falling from a funnel.

The experiment is designed to show that pitch, which can be smashed with a hammer like a brittle solid, will actually flow like a fluid, if you leave it for long enough.

There have only been eight drops since the experiment began, and scientists expect to wait about a decade between drops, says Mainstone, who took over custodianship of the experiment when Parnell died.

"So far nobody has actually observed when the moment at which the drop parts company with the rest of the pitch in the funnel," he says.

"In the year 2000 we thought we had it covered by having the thing under video surveillance," he says. "But unfortunately that new piece of technology failed at the crucial time."

Mainstone admits that some might think his job is worse than watching grass grow or paint try but he is proud to note the experiment is featured in text books.

And he says he is still collecting useful data on the viscosity of pitch, which is about 100 billion times greater than water.